This invention relates to a liquid treatment installation and methods for constructing a liquid treatment installation, and particularly but not exclusively concerns a means for separating solid or liquid particles from a liquid, where said means is arranged to be assembled in situ.
It is known from EP-A-0666769 to provide apparatus in which solid or liquid particles are separated from a liquid by a spiral separator. Spiral separators consist of a number of coaxially helical plates, most preferably in an intertwined multiple helix configuration. These spiral separators may be arranged in a body of liquid to be treated in a tank, and rotated to induce an axial flow of liquid along a number of helical flow paths. The direction of the axial flow depends on whether liquid is added to the tank at the top or the base of the body of liquid. For example, when liquid is added to the tank at the base and drawn off at the top to remove denser solid or liquid impurities, the separator or separators are rotated so as to induce an upflow through the separators. However, as the spiral separators are single components of considerable physical size, their manufacture, transport and installation all prove to be difficult.
It is an object of the present invention to provide a spiral separator which can be constructed from a plurality of smaller components, to reduce the transport and handling problems outlined above.
According to a first aspect of the present invention, there is provided a liquid treatment installation comprising a tank defining a substantially vertical flow channel of circular cross section, a spiral separator comprising one or more conical helical plates defining at least one helical flow passage between axially facing surfaces of the plate or plates, the spiral separator being disposed coaxially in the flow channel, the diameter of the separator being substantially equal to that of the flow channel, the spiral separator being capable of rotating about the axis of the flow channel, an inlet means arranged to supply unseparated liquid to the tank, and an outlet means arranged to withdraw treated liquid from the tank, the inlet and outlet means are vertically spaced in relation to the tank and the arrangement being such that between the inlet and the outlet means the liquid flows vertically through the helical flow passages of the spiral separator, wherein the conical helical plate of the separator comprises a plurality of platelets.
According to a second aspect of the present invention, there is disclosed a spiral separator which comprises a xe2x80x9cplate packxe2x80x9d including a conical helical plate, defining a helical flow passage between axially facing surfaces of the plate, the spiral separator being disposed coaxially in a flow channel of a liquid treatment installation, the diameter of the separator being substantially equal to that of the flow channel, the spiral separator being capable of rotating about the axis of the flow channel, wherein the conical helical plates of the plate pack comprises a plurality of platelets.
According to a third aspect of the present invention, there is disclosed a platelet which is shaped as a sector of an annulus. Two edges are concentrically curved so that a shorter one of the two is concave and the longer curved edge is convex, and the curved edges are joined by a pair of diverging edges extending substantially radially with respect to the concentric edges, the plate also being curved about an axis in the plane of the plate which is perpendicular to the concentric edges. The diverging edges form a leading edge and a trailing edge of said platelet, and when the platelet is in position in a plate pack, the platelet is separated from the top of bottom surfaces of an axially adjacent platelet by a spacing means.
According to an embodiment of the third aspect of the present invention, there is disclosed a platelet which is shaped as a sector of an annuls. Two edges are concentrically curved so that a shorter one of the two is concave and the longer curved edge is convex, and said edges are joined by a pair of diverging edges extending radially with respect to the concentric edges. The diverging edges form a leading edge and a trailing edge of said platelet. The leading edge of the platelet may be offset in the thickness direction of the platelet by a distance substantially equal to the thickness of the platelet so that a continuously smooth upper surface is obtained when adjacent platelets overlap. The platelet is also provided with a flange section, which is situated at the shorter, concave edge of the platelet and forms a cylindrically curved wall fitted concentrically with the concave curved edge. The edge of the flange section remote from the platelet may be radially inset and has one or more recessed portions which are further radially inset. Both the flanges and the radially insert portion of the flange possess locating means, wherein said flange acts as spacing means which, when the platelet is in position in a plate pack, separates the platelet from the top or bottom surface of axially adjacent platelets, and further where said locating means allow axially adjacent platelets to be positioned so that fluid communication is provided between a central axial tube formed by the flanges of adjacent platelets and a flow channel.
According to a fourth aspect of the present invention, there is disclosed a method of constructing a spiral separator, for use in a liquid treatment installation, wherein in a first construction step a plurality of platelets are attached to an annular driving ring to form a first ring of platelets, and in a subsequent construction step platelets are passed through a central opening of the first ring of platelets, and are attached to the platelets that form the first ring.
The advantages of constructing a spiral separator from said platelets is firstly that the separator can be assembled in situ, which eliminates the need for heavy lifting equipment in the transport and installation processes. Furthermore, because the separator consists of an assembly of individual platelets and is not an integral component, then any faults in or damage to the separator can be rectified by replacing the individual faulty or damaged platelets.
The dimensions of the platelets are such that the construction of a spiral separator comprising a plate pack can be carried out inside the flow passage where the plate pack will operate.
In a preferred embodiment, the separator comprises a plurality of conical helical plates which have been formed from the individual platelets and are arranged in an intertwined multiple helix configuration to form a plate pack.
In an advantageous embodiment, the platelets are tapered across their cross section in a direction from the leading edge to the trailing edge or vice versa, so that the overlapping edges of each platelet do not cause thickening at the joints.
In another aspect of the preferred embodiment, the spiral separator may be installed in an existing tank with any non-circular cross section. The existing tank may have any desired shape in plan, and may contain internal filler blocks so that a flow channel of circular cross section is provided.
An advantage of being able to instal the spiral separator in an existing tank is that overall cost is reduced because costs associated with the construction of the tank are eliminated.
In another embodiment, a method of constructing a spiral separator involves attaching, at a working position, a number of platelets to an annular driving ring which is also attached to a lifting means, to form a ring of platelets and, upon completion of the ring, lifting the annular driving ring so that another ring of platelets can be added to the plate pack without moving the working position.
An advantage associated with such a method of construction is that the construction always takes place at the same level (e.g. the bottom of a tank or containing means). In some circumstances, it is more convenient to move the partially complete plate pack as work proceeds than to move a working platform.
Embodiments of the invention will now be described by way of example only and with reference to the accompanying drawings, in which:
FIG. 1 is a schematic diagram showing a plurality of conical helical plates formed from platelets and arranged in an intertwined multiple helix configuration to form a plate pack;
FIG. 2 shows a single platelet;
FIG. 3 shows how two of the platelets of FIG. 2 fit together;
FIG. 4 shows a number of platelets in a different embodiment;
FIG. 5 is a schematic diagram showing a conical helical plate formed from a number of the platelets of FIG. 4;
FIG. 6 shows a sectioned side elevation of the containing means at the initial stage of the plate pack construction in a first method;
FIG. 7 shows a sectioned side elevation of the containing means when plate pack construction has been completed;
FIG. 8 shows a sectioned side elevation of the completed liquid treatment installation;
FIG. 9 shows a sectioned side elevation of the containing means at the initial stage of plate pack construction in a second method;
FIG. 10 shows a sectioned side elevation of the containing means when plate pack construction (second method) is partially complete;
FIG. 11 shows a sectioned side elevation of the containing means when plate pack construction (second method) has been completed and before the annular driving ring is fixed into position; and
FIG. 12 shows a perspective view of a containing means for use in a third method of assembling the plate pack.